The present invention relates generally to a new and novel electromagnetically controlled bi-directional one-way clutch apparatus. More particularly, the present invention relates to a new and novel electromagnetically controlled bi-directional one-way clutch apparatus which is enabled to transmit or cut-off both clockwise and counterclockwise rotation at the input side and can be used, for example, as an "on-demand" torque transmitting device in a part-time four-wheel drive motor vehicle to provide an arrangement for limiting more than a predetermined amount of overrun or differentiation between the front wheels and the rear wheels of a motor vehicle. The electromagnetically controlled bi-directional one-way clutch apparatus in accordance with the present invention allows relative overrun or differentiation between the front wheels and the rear wheels of the motor vehicle up to a predetermined threshold and, thereafter, precludes such relative overrun or differentiation so a portion of the torque being provided to the axle with slipping wheels is redirected and transmitted to the axle with non-slipping wheels.
Four-wheel drive motor vehicles are becoming increasingly popular. Recently, certain motor vehicles have been provided with "full-time" four-wheel drive systems. In such "full-time" four-wheel drive systems, the torque transfer cases are typically provided with an interaxle differential for dividing torque between the front wheels and the rear wheels of the motor vehicle. The interaxle differential enables the front wheels and the rear wheels to rotate at different speeds, which occurs during normal turning of the motor vehicle or in the event that the front wheels and the rear wheels have tires with different diameters. However, to prevent excessive relative slipping between the front wheels and the rear wheels, as might occur when one set of wheels encounters a low-traction condition, such as ice, these transfer cases typically include a selectively engageable clutch which is operative to lock the interaxle differential upon sensing a predetermined amount of relative slippage between the front output shaft and the rear output shaft of the transfer case. Locking of the interaxle differential prevents any further relative overrun or differentiation between the front output shaft and the rear output shaft of the transfer case.
Known prior "full-time" four-wheel drive systems have generally required complex electronic sensors or other complex systems to monitor the overrun or differentiation between the front output shaft and the rear output shaft or the front wheels and the rear wheels of a motor vehicle. Upon sensing relative overrun or differentiation, an electronic control system determines whether the relative overrun or differentiation being encountered is within a "normal" expected range or is "excessive." If the electronic control system indicates that the overrun or differentiation being experienced is "excessive," the electronic control system causes the selectively engageable clutch to lock the interaxle differential to preclude any further relative overrun or differentiation. An electronic control system of this type can be expensive to manufacture and maintain and a more cost-effective, simplified "on demand" system of limiting more than a predetermined amount of overrun or differentiation between the front wheels and the rear wheels of the motor vehicle would be desirable.
A preferred embodiment of the present invention is, therefore, directed to an electromagnetically controlled bi-directional one-way clutch apparatus which permits relative overrun or differentiation between a front torque transmitting shaft and a rear torque transmitting shaft up to a predetermined level and, if the amount of relative overrun or differentiation between the front torque transmitting shaft and the rear torque transmitting shaft exceeds this predetermined level, locks the front torque transmitting shaft and the rear torque transmitting shaft together such that the front torque transmitting shaft and the rear torque transmitting shaft rotate at substantially the same rotational speed. This electromagnetically controlled bi-directional one-way clutch apparatus is particularly useful for use in an "on demand" four-wheel drive system for a motor vehicle having an engine and a front wheel drive transaxle assembly where the electromagnetically controlled bi-directional one-way clutch acts as a torque transmitting device which allows relative overrun or differentiation between the front wheels and the rear wheels of the motor vehicle up to a predetermined level and, if the amount of relative overrun or differentiation between the front wheels and the rear wheels of the motor vehicle exceeds this predetermined level, locks the front wheels and the rear wheels of the motor vehicle together such that the front wheels and the rear wheels of the motor vehicle rotate at substantially the same rotational speed. The electromagnetically controlled bi-directional one-way clutch apparatus preferably includes a first torque transmitting shaft coupled to the transmission or transaxle assembly such that the first torque transmitting shaft is rotatably driven by the transmission or transaxle assembly and transmits torque to the front axle of the motor vehicle and a second torque transmitting shaft which is rotatably coupled to the rear axle of the motor vehicle. If the rotational speed of the front wheels overrides the rotational speed of the rear wheels by less than a predetermined amount, say 20%, electromagnetically controlled bi-directional one-way clutch apparatus does not engage and relative overrun or differentiation between the front wheels and the rear wheels is permitted. However, if the rotational speed of the front wheels overrides the rotational speed of the rear wheels by more than the predetermined amount, for example, when the front wheels of the motor vehicle are on ice, snow, mud or some other slippery surface, electromagnetically controlled bi-directional one-way clutch apparatus locks the front wheels and the rear wheels of the motor vehicle together to transmit a portion of the torque being provided to the excessively overrunning or differentiating front wheels to the rear wheels and cause the front wheels and the rear wheels to rotate together at substantially the same rotational speed.
Accordingly, the present invention provides an arrangement for permitting a first torque transmitting shaft to overrun or differentiate up to a predetermined amount in relation to a second torque transmitting shaft, but when the first torque transmitting shaft overruns or differentiates greater than this predetermined amount in relation to the second torque transmitting shaft, the electromagnetically controlled bi-directional one-way clutch apparatus locks the first torque transmitting shaft and the second torque transmitting shaft together to rotate at substantially the same rotational speed.
In addition, the electromagnetically controlled bi-directional one-way clutch apparatus in accordance with the present invention enables transmission or cut-off of both clockwise and counterclockwise rotation at the input side. The electromagnetically controlled bi-directional one-way clutch apparatus in accordance with the present invention is also capable of engaging or disengaging auxiliary driving wheels to switch back and forth between two-wheel drive and four-wheel drive during vehicle operation. In this regard, the electromagnetically controlled bi-directional one-way clutch apparatus may be used in a transfer case which provides power for the auxiliary driving wheels.
In fact, the electromagnetically controlled bi-directional one-way clutch apparatus in accordance with the present invention is useful in any arrangement where the speeds of the driving member and the driven member are nearly synchronous and multiple modes of operation are desired. For example, the electromagnetically controlled bi-directional one-way clutch apparatus in accordance with the present invention can completely disengage the auxiliary driving wheels for two-wheel drive for normal highway vehicle operations, positively lock the auxiliary driving wheels for four-wheel drive for low speed, off-highway vehicle operations or automatically engage the auxiliary driving wheels in response to vehicle operating conditions, such as slippage of the primary drive wheels. In addition, the electromagnetically controlled bi-directional one-way clutch apparatus in accordance with the present invention provides for easy and gentle transition between its operational modes.
Other advantages and novel features of the present invention will become apparent in the following detailed description of the invention when considered in conjunction with the accompanying drawings.